Protective system for electric blankets



July 22, 1947.

J. W. DOWNlE PROTECTIVE SYSTEM FOR ELECTRIC BLANKETS .Filed Nov. 1, 1944 'Invehbow- John W. Downie His Attorney.

Patented July 22, 1947 PROTECTIVE SYSTEI FOR ELECTRIC BLANKETS John W. Downie, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application November 1, 1944, Serial No. 561,363

4 Claims.

This invention relates to protective systems, more particularly to such a system for protecting an electrically-heated blanket used upon a bedstead, and it has for its object the provision of improved protective means of this character,

Certain electric blankets now found upon the market comprise a blanket having channels woven or stitched therein through which is threaded an electric heating conductor. The conductor is energized from a suitable source of electrical supply and generates sufiicient heat to keep the blanket at some desired temperature under normal conditions of operation during which the blanket is spread out over the bed. It occasionally happens that in the morning the occupant gets up and folds the blanket up at the foot of the bed without disconnecting the blanket from the supply source. As a result the heat lost from a section of the heating conductor is greatly reduced and this tends to cause localized heating with the attendant possibility of fire. In order to preclude the possibility of such local overheating, there has been incorporated into the blanket a number of protective thermostats which are suitably placed in different areas and connected so that overheating in any one of these areas causes the associated thermostat to operate to deenergize the blanket. At times the excessive overheating occurs in a part of the blanket which does not have a protective thermostat. At other times some difficulty has arisen because the safety thermostats themselves have failed to function.

This invention contemplates an improved protective system for blankets which, with the exception of a relatively short preliminary heating period, prevents the energization of the blanket as long as the bed is unoccupied, regardless of the fact that the blanket may be plugged in to its supply source. However, whenever the bed is occupied the system conditions the blanket for energization.

Also, as intimated above, this invention contemplates such a system arranged so that it is conditioned to effect the heating of the blanket for a predetermined preliminary period merely by momentarily loading the bed; that is, by pressing down on the bed or by lying on it for a moment and then unloading or releasing it, the cbntrol will be conditioned to cause heating of the blanket for a selected period of time such as 30 or 40 minutes or so; this provides for a preliminary heating period for the bed so that it may be warmed up prior to retiring.

More specifically, this system comprises a circuit controlling device connected in the blanket heating circuit and operated responsively to the flexing of the mattress support. When the bed is unoccupied and the support unflexed the circuit control device opens the blanket circuit. However, when the support is flexed due to the weight of a person in the bed the control device completes the circuit through the control device and conditions the blanket for energization, Moreover, once the control device has been operated to energize the blanket it will keep it energized for a predetermined period of time after the bed is unloaded. This is for the purpose of giving the preliminary heating period referred to above.

For a more complete understanding of this invention, reference should be had to the accompanying drawing in which Fig. 1 is a plan view of a bed provided with an electric blanket embodying the protective system of this invention, parts of the bed and blanket being broken away so as to illustrate certain structural details; Fig. 2 is an enlarged fragmentary sectional view taken through a portion of the bed shown in Fig. 1; Fig. 3 is a view similar to Fig. 2 but illustrating certain elements in different operative positions than they occupy in Fig. 2; Fig. 4 is a fragmentary view showing certain of the elements of Figs. 2 and 3 but in a different operative condition; Fig. 5 is a perspective View of a controlling element used in this protective system; and Fig. 6 is a diagrammatic plan view of the electrically heated blanket, and of certain temperature controlling mechanism therefor, and further, illustrating the protective means provided therefor and arranged in accordance with this invention.

Referring to the drawing, this invention has been shown in connection with a bed I provided with supporting end heads 2 and 3, and a bed spring 4 having the usual wire mesh 5 anchored to a supporting frame 6 by means of spiral springs I. Mounted upon the bed spring 4 is a suitable mattress 8, and positioned normally to cover the mattress 8 is an electrically heated blanket 9. The blanket 9 is provided with a resistance heating Conductor H) which is formed into a series of convolutions H extending throughout substantially the full area of the blanket, as shown in Figs. 1 and 6. It will be understood that the conductor l0 preferably will be threaded through suitable channels (not shown) provided for it in the blanket, which channels may be formed by stitching or weaving them into the blanket itself. Connected into the energizing circuit of the heating resistance ID are a plurality of suitable protective thermostats l2 (not constituting a part of this invention), which thermostats are connected in series with the conductor, as shown, and which are placed Within the blanket in heat conducting relation therewith and set to operate in response to an abnormally high temperature to deenergize the resistance conductor. While six of these thermostats have been shown, it will be understood that any suitable number may be used.

The heating conductor 15 is energized from a suitable source of electrical supply [3 through a manually operable control switch l4 and a suitable temperature responsive controlling device l5 located in the bedroom to respond to its temperature. This control device comprises a switch it connected in series with the heating resistance ltl, which switch is operated by means of a bimetallic temperatur responsive element IT. The bimetallic element i7 is heated by a local heater :8 as well as by the temperature of the room in which the blanket is located. One end of the resistance 58 is connected to one conductor of the supply source 53, while the other end is connected to the other conductor through the switch contacts 16 and the switch 14, as clearly shown in Fig. 6. This system of control is described. and broadly claimed in the patent to W. K. Kearsley No, 2,195,958, dated April 2, 1940, and reference is made thereto for a more complete description of the control system.

The protective system arranged in accordance with this invention prevents undesired energization of the blanket 9 when the bed is not used, but conditions the blanket for normal operation when the bed is occupied. This means comprises a switch iii connected in series with the resistance conductor ill, as shown in Fig. 6.

The switch l8 comprises a casing 25 which is suspended from the mesh 5 by means of supporting arms 2!. Mounted within the casing iii is an elongated envelope 22 within the end portions of which are a pair of spaced fixed contacts 23 which are connected into the circuit of the resistance conductor it as clearly shown in Fig. 6. Preferably the lower half 24 (Fig. 5) of the envelope will be formed of metal, while the upper half 25 will be formed of glass; and preferably the contacts will enter the casing through the top wall of this glass upper half. Within the envelope there is a pool 28 of electrically-conducting liquid material such as mercury, this pool constituting liquid contacting means for making and breaking contact between the two spaced contacts 23. Also located Within the casing about midway between its ends is a transverse partition 2? located midway between the ends of the casing and dividing the lower half thereof into two parts of substantially equal volume. This partition wall 2! has several relatively small apertures 23 extending therethrough; and in addition there is a tube 29 having one end passing through the lower part of the partition and its other end curved upwardly in the right-hand end of the envelope, as shown.

The envelope 22 is mounted within a suitable ring support 39 which is pivotally mounted in the casing l9 and the position of which with reference to the casing may be adjusted by means of a thumb screw 3!. As shown the support 39 is provided -with an extension 32 which is biased against the thumb screw 3! by means of a tension spring 33.

It will be observed that the casing i9 is positioned crosswise of the bed so that the envelope 22 is also positioned crosswise thereof, as shown in Fig. 2. When the bed is unoccupied and the bed spring 4 unflexed the pool of mercury 26 will be in its position shown in Fig. 2 wherein the circuit between the contacts 23 is broken. Under such conditions, the blanket cannot be energized, irrespective of the fact that the switch 14 and the switch contacts 56 of the thermal control d vice I 5 be closed.

However, when a person gets into the bed the bed spring flexes downwardly, as is well understood, and when this happens the casin 19 tilts from its position of Fig. 2 to its position of Fig, 3. This tilts the envelope 22 and permits the pool of mercury 25 freely to flow through pipe 29 and attain a uniform level through both end portions of the envelope and thereby make contact with both contacts 23, as shown in Fig. 3; this operation closes the circuit to the resistance conductor ID through the control device [9. Therefore, the blanket may function in the normal manner to heat up under the control of the control device l5, and as long as the bed is occupied the circuit will be completed through the control device l9.

When the bed occupant gets up, the mattress. of course is unloaded, and as a result the bed spring 4 returns the envelope 22 to its position of Fig. 1. But because of the partition 2'! the mercury pool is divided, part thereof being dammed on the right side of the partition, as shown in Fig. 4. This maintains the blanket circuit closed, and it will do so until enough of the mercury in the right side leaks through the openings 23 in the partition to the left side of the partition to uncover the right-hand electrode 23, as shown in Fig. 2. When this happens the blanket circuit is interrupted. The opening 23 have such a size that the blanket will remain energized for 30 to 40 minutes or for some other suitable period of time which is sufficient to heat up the blanket and mattress initially. The advantage of this is that by momentarily loading the mattress 30 or 40 minutes prior to retiring, the blanket will be energized and remain energized for that period so as to heat up the bed prior to retiring so that it is nice and warm when the occupant gets into the bed. After that the system will function as fully described above.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I therefore aim in the appended claims to cover all such changes and modifications as fall within th true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a bed, an electric heating member for heating a person reclining on said bed, said heating member having a heating circuit, safety switch means connected in said circuit to control said heating member operated to close said circuit by the loading of said bed due to the weight of a person reclining thereon, and to open said circuit in response to the unloading of said bed, and time-delay means controlling said switch to delay the opening of said circuit so that said circuit can be closed to heat said bed for a predetermined time interval by loading said bed momentarily and then unloading it.

2. In combination, a bed having a mattress, a flexible bed spring supporting said mattress, an electrically heated blanket covering said mattress for heating a person reclining on the mattress, said blanket having a heating circuit,thermallyresponsive switchmeans responsive to the air temperature of the room in which said bed and blanket are located connected in said circuit for energizing and deenergizing it responsively to variations in said air temperature so as to hold a substantially constant temperature in said blanket, and an auxiliary circuit controlling safety device electrically connected in said heating circuit to open and close it comprising a closing casing mounted upon said bed spring, a pair of spaced contacts in said casing, and fluid contact means also within said casing normally out of bridging contact with both of said contacts when the bed spring is unflexed, but when said bed spring is flexed downwardly a predetermined degree due to the loading of the mattress by a person getting into said bed said casing is tilted to cause said liquid contact means to bridge both of said contacts thereby to close the circuit through said safety device, and when said mattress is unloaded by the person leaving said bed said casing is tilted to cause the liquid contact means to break said contacts to reopen said circuit, irrespective of the temperature of the air in said room and its effect upon said thermally responsive switch.

3. In combination, a bed having a mattress, a flexible bed spring for said mattress, an electrically heated blanket covering said mattress for heating a person reclining on the mattress, said blanket having a heating circuit, and a circuit controlling safety switch electrically connected in said heating circuit to open and close it comprising a switch member connected in said circuit and also connected to said bed spring so as to be operated by its flexing'and unflexing to close said circuit through said safety device when said bed spring is flexed down a predetermined degree by a person getting into said bed, and to open said circuit through said safety device when said spring unflexes responsively to the unloading of said mattress when the person gets out of said bed, and time-delay means controlling said switch to delay the opening of said circuit so that said circuit can be closed to heat said bed for a predetermined time interval by momentarily loading said mattress and then unloading it 4. In combination, a bed having a mattress, a flexible bed spring supporting said mattress, an electrically-heated blanket over said mattress having a heating circuit, and a circuit controlling device electrically connected in said heating circuit to open and close it comprising a closed casing mounted upon said bed spring, a pair of spaced contacts in said casing, fluid contact means also within said casing normally out of bridging contact with both of said contacts when the bed spring i unflexed, but when said bed spring is flexed downwardly a predetermined degree due to the loading of the mattress said casing is tilted to cause said liquid contact means to flow and bridge both of said contacts to close the circuit through said control device, and a partition within said casing between said contacts provided with apertures to control the rate of flow of said liquid contact means to break contact with one of said contacts when said spring is unfleXed and the casing tilted back so that said blanket circuit remains closed through said controlling device for a predetermined interval of time after said spring is unflexed.

JOHN W. DOWNIE.

REFERENCES CITED The following references file of this patent:

UNITED STATES PATENTS are of record in the 

